Infrared spectrum of the CH3OH - CO complex in the C-O stretching region

The infrared spectrum of the weakly-bound molecular complex methanol - carbon monoxide has been observed, for the first time in the gas phase, by means of a parallel (D K = 0) band in the region of the carbon monoxide C-O stretching vibration. The band origin, 2154.5 cm-1, represents a blue shift of 11.2 cm-1 relative to the free CO molecule; its proximity to that of the H2O - CO complex points to a similarity of the hydrogen bonding in the two systems. The observed structure of the band could be well reproduced by a simulation based on the methyl internal rotation component of Asymmetry. A component of E-symmetry must also be present, with roughly equal intensity, but the two components were not individually resolved. The observed transitions showed evidence of predissociation broadening, leading to an estimate of t 0.5 ns for the lifetime of the upper (C-O stretching) state.